This invention relates to an apparatus for forming, punching and positioning a continuous key joint strip and automatically inserting tie bars, which apparatus is particularly useful in combination with a slip-form roadway paver to form and position a continuous key joint with bars placed in proper position and with a pavement being formed in a continuous fashion as the paver moves forwardly over a road bed.
In building roads and highways it is common practice to construct the road by forming concrete slabs arranged in side-by-side relation. In connecting these adjacent slabs, the road building industry has adopted the use of keys and key slots at the abutting side edges of adjacent concrete slabs. Steel tie rods or bars are often mounted in conjunction with the key slots to prevent separation of the slabs. The common practice used to develop these key slots has been to mount a mold or key strip to the inner face of a road form. When using steel tie bars, half of the bar extends into the formed slab and the other half of the bar is bent 90.degree. and hidden within the key slot on the inner face of the road form. After the cast slab has hardened, the key strips are removed and the tie bars may later be straightened out to provide connection with the adjacent slab. This method was considered generally satisfactory with prior art road forming equipment where the roads were formed section-by-section rather than continuously as is now possible with modern and faster paving machines such as those known as slip form pavers.
In using a slip form paver, a concrete slab is formed in an automatic continuous fashion. As a result, the aforementioned prior art methods of forming key joints are entirely inadequate in that the advantages of speed and simplicity of the slip form paver are defeated by using the prior art step-by-step methods of forming the key joints.
U.S. Pat. No. 3,491,661 discloses an apparatus for automatically forming slip form keyway joints and U.S. Pat. No. 3,530,776 discloses an apparatus for automatically placing tie bars in such a keyway. The problem with such structures is that they are unduly complicated and if such structures malfunction, the keyway is torn out, which is a very costly, timely, and complicated situation to solve.